Blank thinning predictions of an aluminum alloy in hole expansion process using finite element method

Mehmet Firat,Toros Arda Akşen

doi:10.1007/s42452-021-04336-7

Abstract

The main objective of this study is to accurately predict the thinning behavior of AA6016-O aluminum alloy in the hole expansion test. In order to perform this aim, three yield functions, namely isotropic von Mises, quadratic Hill48 and non-quadratic Yld91, are considered and their prediction capabilities are evaluated in this study. Firstly, finite element (FE) model of hole expansion test is created by implicit FE software Marc, then FE simulations are performed with each yield criterion. In order to assess prediction capabilities of these yield criteria, thickness strain distributions along the three directions of the sheet (rolling, diagonal and transversal) and punch force–displacement curves are investigated. The results predicted from FE analyses are compared with experimental results. From the comparisons, it is observed that Yld91 yield criterion could successfully predict the thickness strain distributions along the rolling and transverse directions, whereas the other two criteria could only predict the thickness strain distributions along the diagonal direction. On the other hand, it is determined that punch force–displacement curves predicted from three models are identical and these predictions are overestimated compared to experimental data.

Highlights

Aluminum alloys are widely used metals in automotive industry due to their mechanical properties
hole expansion test (HET) was modeled in implicit finite element (FE) code Marc and FE analyses of the test were performed with von Mises, Hill48 and Yld91 yield functions
HET of AA6016-0 aluminum alloy was modeled and FE simulations were performed with von Mises, Hill48 and Yld91 yield criteria

Summary

Introduction

Aluminum alloys are widely used metals in automotive industry due to their mechanical properties. They reduce the body weight of the automobile and provide sufficient strength due to their strength-to-weight ratios. They exhibit low ductility and prone to fracture [1]. It is important to understand the formability limits of the aluminum alloy sheets. Uniaxial tensile test is an important test providing fundamental mechanical properties, but it cannot estimate the stretch flange formability limits [2]. To predict the features of the stretch flange formability, several tests are conducted such as Nakajima test, Marciniak test or hole expansion test (HET). It is recorded that the uniaxial stress state occurs in a narrow range and stress state changes from uniaxial tension at the hole edge to balanced biaxial tension at the outer periphery of the blank [3]

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Conclusion